U.S. patent number 7,449,957 [Application Number 11/435,891] was granted by the patent office on 2008-11-11 for radio frequency power amplifier.
This patent grant is currently assigned to Panasonic Corporation. Invention is credited to Shingo Enomoto, Masahiko Inamori, Katuhiko Kawashima, Haruhiko Koizumi, Hirokazu Makihara, Shingo Matuda, Kazuki Tateoka.
United States Patent |
7,449,957 |
Enomoto , et al. |
November 11, 2008 |
Radio frequency power amplifier
Abstract
A radio frequency signal RF is input to a base of each of
transistors TR1 through TRn via a corresponding capacitor among
capacitors C1 through Cn, is amplified, and is output from a
collector of each of the transistors TR1 through TRn. An emitter of
each of the transistors TR1 through TRn is grounded. A bias voltage
DC given from a bias circuit Bias is supplied to the base of each
of the transistors TR1 through TRn via a corresponding resistor
among resistors Ra1 through Ran. A signal line for the bias voltage
DC is connected to an input line for the radio frequency signal RF
via the bridge resistor R in a direct current manner.
Inventors: |
Enomoto; Shingo (Osaka,
JP), Inamori; Masahiko (Osaka, JP),
Koizumi; Haruhiko (Osaka, JP), Tateoka; Kazuki
(Kyoto, JP), Makihara; Hirokazu (Osaka,
JP), Matuda; Shingo (Kyoto, JP), Kawashima;
Katuhiko (Hyogo, JP) |
Assignee: |
Panasonic Corporation (Osaka,
JP)
|
Family
ID: |
36709591 |
Appl.
No.: |
11/435,891 |
Filed: |
May 18, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20060261897 A1 |
Nov 23, 2006 |
|
Foreign Application Priority Data
|
|
|
|
|
May 20, 2005 [JP] |
|
|
2005-148103 |
|
Current U.S.
Class: |
330/295;
330/302 |
Current CPC
Class: |
H03F
1/30 (20130101); H03F 3/189 (20130101); H03F
3/20 (20130101); H03F 2203/21178 (20130101) |
Current International
Class: |
H03F
3/68 (20060101); H03F 3/191 (20060101) |
Field of
Search: |
;330/295,302,258
;327/143 ;300/295,302 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
European Search Report issued in corresponding European Patent
Application No. EP 06 01 0419.7, dated Aug. 14, 2006. cited by
other.
|
Primary Examiner: Pascal; Robert
Assistant Examiner: Nguyen; Khiem D
Attorney, Agent or Firm: McDermott Will & Emery LLP
Claims
What is claimed is:
1. A radio frequency power amplifier usable for power amplification
of a radio frequency signal, the radio frequency power amplifier
comprising: a plurality of transistors connected in parallel and
each having a grounded emitter; a plurality of first resistors each
having one terminal commonly supplied with a direct current bias
voltage and the other terminal connected to a base of the
corresponding transistor among the plurality of transistors; a
plurality of capacitors each having one electrode for commonly
receiving the radio frequency signal and the other electrode
connected to the base of the corresponding transistor among the
plurality of transistors; and at least one bridge resistor for
connecting the one terminal of each of the plurality of first
resistors and the one electrode of each of the plurality of
capacitors.
2. A radio frequency power amplifier usable for power amplification
of a radio frequency signal, the radio frequency power amplifier
comprising: a plurality of transistors connected in parallel and
each having a grounded emitter; a plurality of first resistors each
having one terminal commonly supplied with a direct current bias
voltage and the other terminal connected to a base of the
corresponding transistor among the plurality of transistors; a
capacitor having one electrode for receiving the radio frequency
signal and the other electrode connected to a base of each of the
plurality of transistors; and at least one bridge resistor for
connecting the one terminal of each of the plurality of first
resistors and the one electrode of the capacitor.
3. A radio frequency power amplifier according to claim 1, further
comprising a plurality of second resistors each inserted between a
connection point of the other terminal of the corresponding
resistor among the plurality of first resistors and the other
electrode of the corresponding capacitor among the plurality of
capacitors, and the base of the corresponding transistor among the
plurality of transistors.
4. A radio frequency power amplifier according to claim 2, further
comprising a plurality of second resistors each inserted between a
connection point of the other terminal of the corresponding
resistor among the plurality of first resistors and the other
electrode of the capacitor, and the base of the corresponding
transistor among the plurality of transistors.
5. A radio frequency power amplifier according to claim 1, further
comprising a plurality of second resistors each inserted between
the other electrode of the corresponding capacitor among the
plurality of capacitors, and a connection point of the other
terminal of the corresponding resistor among the plurality of first
resistors and the base of the corresponding transistor among the
plurality of transistors.
6. A radio frequency power amplifier according to claim 2, further
comprising a plurality of second resistors each inserted between
the other electrode of the capacitor, and a connection point of the
other terminal of the corresponding resistor among the plurality of
first resistors and the base of the corresponding transistor among
the plurality of transistors.
7. A radio frequency power amplifier according to claim 1, further
comprising a plurality of second resistors each inserted between a
terminal of the at least one bridge resistor, to which the radio
frequency signal is input, and the one electrode of the
corresponding capacitor among the plurality of capacitors.
8. A radio frequency power amplifier according to claim 2, further
comprising a second resistor inserted between a terminal of the at
least one bridge resistor, to which the radio frequency signal is
input, and the one electrode of the capacitor.
9. A radio frequency power amplifier according to claim 7, each
include a transmission line wherein a plurality of transmission
lines act as the plurality of second resistors.
10. A radio frequency power amplifier according to claim 8, wherein
a transmission line acts as the second resistor.
11. A radio frequency power amplifier according to claim 1,
comprising a plurality of bridge resistors respectively provided in
correspondence with the plurality of first resistors.
12. A radio frequency power amplifier according to claim 2,
comprising a plurality of bridge resistors respectively provided in
correspondence with the plurality of first resistors.
13. A radio frequency power amplifier according to claim 1, wherein
the direct current bias voltage is supplied from a bias circuit
which uses an emitter follower as an output structure.
14. A radio frequency power amplifier according to claim 2, wherein
the direct current bias voltage is supplied from a bias circuit
which uses an emitter follower as an output structure.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio frequency power amplifier
suitable for power amplification of a radio frequency signal.
2. Description of the Background Art
An amplifier used for a wireless communication device such as a
mobile phone or the like generally uses a structure in which a
plurality of, for example, two or three, compound semiconductor
transistors for radio frequency amplification are connected to each
other. As such a compound semiconductor transistor, a
hetero-junction bipolar transistor has mainly been used recently
for the reason regarding the single positive power source operation
or the like. A final-stage amplifier for a mobile phone having an
output power of about 1 to 3 W is provided by connecting a
plurality of transistors in parallel to combine the outputs from
the transistors, in order to obtain radio frequency characteristics
and a high output. FIG. 10 shows an example of a conventional radio
frequency power amplifier 100 having such a structure. See, for
example, U.S. Pat. Nos. 5,321,279 and 5,608,353.
With the conventional radio frequency power amplifier 100 shown in
FIG. 10, a direct current bias voltage (DC) given from a bias
circuit (Bias) is supplied to bases (B) of transistors TR101
through TR10n via corresponding resistors Ra101 through Ra10n. A
radio frequency signal (RF), which is an AC signal, is input to the
bases of the transistors TR101 through TR10n via corresponding
capacitors C101 through C10n. The reason why the bias voltage (DC)
and the radio frequency signal (RF) are input to the bases of the
transistors TR101 through TR10n via separate paths is as
follows.
The transistors TR101 through TR10n generate heat when performing a
high output operation because the current density of the AC current
is raised. The heat generation is not uniform among all the
transistors TR101 through TR10n due to a characteristic dispersion
among the transistors TR101 through TR10n or the like. A specific
transistor having a high temperature may cause thermal runaway due
to excessive heat generation during operation and destroy the
device due to an increase in the base current. According to a
conceivable technique for suppressing the thermal runaway, when
base voltages of the transistors TR101 through TR10n increase, the
resistance values of the resistors Ra101 through Ra10n are
increased such that the base bias current supplied from the bias
circuit (Bias) decreases.
In the above-described radio frequency power amplifier 100, the
thermal runaway of the transistors Ra101 through Ra10n is
suppressed and thus uniform operation thereof is realized by
increasing the resistance values of the resistors Ra101 through
Ra10n.
However, the resistance values of the resistors Ra101 through Ra10n
cannot be very large because excessively large resistance values of
the resistors Ra101 through Ra10n decrease a power gain of a radio
frequency signal. Namely, the operation uniformity among the
transistors TR101 through TR10n improved by increasing the
resistance values of the resistors Ra101 through Ra10n (improvement
in the destruction resistance) contradicts the radio frequency
power gain improved by decreasing the resistance values of the
resistors Ra101 through Ra10n (improvement in the radio frequency
characteristics). It is very difficult to improve both.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a radio
frequency power amplifier providing both of a sufficient
destruction resistance and superb radio frequency
characteristics.
The present invention is directed to a radio frequency power
amplifier usable for power amplification of a radio frequency
signal. In order to attain the object mentioned above, the radio
frequency power amplifier according to the present invention
comprises a plurality of transistors connected in parallel and each
having a grounded emitter; a plurality of resistors each having one
terminal commonly supplied with a direct current bias voltage and
the other terminal connected to a base of the corresponding
transistor among the plurality of transistors; a plurality of
capacitors each having one electrode for commonly receiving the
radio frequency signal and the other electrode connected to the
base of the corresponding transistor among the plurality of
transistors; and at least one bridge resistor for connecting the
one terminal of each of the plurality of resistors and the one
electrode of each of the plurality of capacitors.
It is not absolutely necessary that a plurality of capacitors are
provided. The radio frequency signal may be input to the bases of
the plurality of transistors via one capacitor. A plurality of
bridge resistors may be provided respectively in correspondence
with the plurality of resistors. Typically, a direct current bias
voltage is supplied from a bias circuit which uses an emitter
follower as an output structure.
Preferably, a plurality of second resistors are each inserted
between a connection point of the other terminal of the
corresponding resistor among the plurality of resistors and the
other electrode of one capacitor or the corresponding capacitor
among the plurality of capacitors, and the base of the
corresponding transistor among the plurality of transistors.
Alternatively, a plurality of second resistors are each inserted
between the other electrode of one capacitor or the corresponding
capacitor among the plurality of capacitors and the base of the
corresponding transistor among the plurality of transistors. Still
alternatively, a plurality of second resistors are each inserted
between a terminal of the at least one bridge resistor, to which
the radio frequency signal is input, and the one electrode of one
capacitor or the corresponding capacitor among the plurality of
capacitors. In this case, the second resistances may each include a
transmission line.
According to the present invention, a radio frequency power
amplifier including a plurality of transistors connected in
parallel further comprises one or a plurality of bridge resistors.
Thus, both of a sufficient destruction resistance and superb radio
frequency characteristics are provided.
These and other objects, features, aspects and advantages of the
present invention will become more apparent from the following
detailed description of the present invention when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a circuit configuration of a radio frequency power
amplifier 1 according to a first embodiment of the present
invention;
FIG. 2 shows an example of a bias circuit (Bias);
FIG. 3A illustrates the relationship between the resistance value
of resistors Ra1 through Ran and the output power Pout;
FIG. 3B illustrates the relationship between the resistance value
of the resistors Ra1 through Ran and the power-added efficiency
PAE;
FIG. 3C shows parameters used for the simulation shown in FIG. 3A
and FIG. 3B;
FIG. 4 shows a circuit configuration of another radio frequency
power amplifier 1' according to the first embodiment of the present
invention;
FIG. 5 shows a circuit configuration of still another radio
frequency power amplifier 1'' according to the first embodiment of
the present invention;
FIG. 6 shows a circuit configuration of a radio frequency power
amplifier 2 according to a second embodiment of the present
invention;
FIG. 7 shows a circuit configuration of a radio frequency power
amplifier 3 according to a third embodiment of the present
invention;
FIG. 8 shows a circuit configuration of a radio frequency power
amplifier 4 according to a fourth embodiment of the present
invention;
FIG. 9 shows a circuit configuration of a radio frequency power
amplifier 5 according to a fifth embodiment of the present
invention; and
FIG. 10 shows a circuit configuration of a conventional radio
frequency power amplifier 100.
FIG. 11 shows a modified circuit configuration of the second
embodiment of the present invention shown in FIG. 6.
FIG. 12 shows a modified circuit configuration of the third
embodiment of the present invention shown in FIG. 7.
FIG. 13 shows a modified circuit configuration of the fourth
embodiment of the present invention shown in FIG. 8.
FIG. 14 shows a modified circuit configuration of the first
embodiment of the present invention shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
FIG. 1 shows a circuit configuration of a radio frequency power
amplifier 1 according to a first embodiment of the present
invention. As shown in FIG. 1, the radio frequency power amplifier
1 according to the first embodiment includes transistors TR1
through TRn, capacitors C1 through Cn, resistors Ra1 through Ran,
and a bridge resistor R. Herein, n is an integer equal to or
greater than two. As the transistors TR1 through TRn,
hetero-junction bipolar transistors using a compound semiconductor
(InGaP) or other types of transistors using Si or SiGe are
usable.
A radio frequency signal (RF), which is an AC signal, is input to a
base (B) of each of the transistors TR1 through TRn via the
corresponding capacitor among the capacitors C1 through Cn, is
amplified, and is output from a collector (C) of each of the
transistors TR1 through TRn. An emitter (E) of each of the
transistors TR1 through TRn is grounded. A direct current bias
voltage (DC) given from a bias circuit (Bias) is supplied to the
base of each of the transistors TR1 through TRn via the
corresponding resistor among the resistors Ra1 through Ran. A
signal line for the bias voltage (DC) is connected to an input line
for the radio frequency signal (RF) via the bridge resistor R in a
direct current manner. The bias circuit (Bias) may have any
structure which can supply a bias voltage (DC).
For example, an emitter follower circuit shown in FIG. 2 may be
preferable as the bias circuit (Bias). The bias circuit (Bias)
shown in FIG. 2 includes a transistor TRB3 acting as an emitter
follower, a resistor RB1 for compensating for a temperature
characteristic, resistors RB2 and RB3 for correcting a bias circuit
characteristic, and transistors TRB1 and TRB2. The transistors TRB1
and TRB2 are each used as a base-emitter diode with the base and
the collector being short circuited, in order to compensate for a
sum of base-emitter voltages between the transistors TR1 through
TRn and the transistor TRB3. The resistors RB2 and RB3 may be
omitted.
An operation of the radio frequency power amplifier 1 according to
the first embodiment having the above-described structure will be
described.
Since the bridge resistor R is inserted, a radio frequency signal
(RF) is input to the base of each of the transistors TR1 through
TRn via a path passing through the bridge resistor R and each of
the resistors Ra1 through Ran as well as via a conventional path
passing through each of the capacitors C1 through Cn. Owing to the
path passing through the bridge resistor R and the resistors Ra1
through Ran, the radio frequency signal (RF) is input toward the
bias circuit (Bias) via the bridge resistor R.
Because of the nonlinearity of a base-emitter diode of the
transistor TRB3, the voltage amplitude of the radio frequency
signal (RF) which is input toward the bias circuit (Bias) is
clipped at the time when the base-emitter diode of the transistor
TRB3 is turned on (negative amplitude), but is not clipped at the
time when the base-emitter diode of the transistor TRB3 is turned
off (positive amplitude). As a result, a positive direct current
offset voltage is generated at a connection point P between the
bridge resistor R and the resistors Ra1 through Ran. The effect of
the positive direct current offset voltage is more conspicuous as
the input power of the radio frequency signal (RF) is larger.
With reference to FIG. 3A and FIG. 3B, the difference between the
effect provided by the radio frequency power amplifier 1 according
to the first embodiment and the effect provided by the conventional
radio frequency power amplifier 100 (FIG. 10) will be described.
The parameters used for the simulation in FIG. 3A and FIG. 3B are
as shown in FIG. 3C.
FIG. 3A shows the output power Pout when the resistance value of
the resistors Ra1 through Ran is variable where the resistance
value of the bridge resistor R is 25.OMEGA. or 50.OMEGA.. FIG. 3B
shows the power-added efficiency PAE when the resistance value of
the resistors Ra1 through Ran is variable where the resistance
value of the bridge resistor R is 25.OMEGA. or 50.OMEGA.. As can be
appreciated from FIG. 3A and FIG. 3B, with the conventional radio
frequency power amplifier 100, the characteristics drastically
deteriorate approximately when the resistance value exceeds
1000.OMEGA.. By contrast, with the radio frequency power amplifier
1 according to the first embodiment, the characteristics do not
deteriorate much even when the resistance value is about
2000.OMEGA.. When the resistance value is about 2000.OMEGA., the
radio frequency power amplifier 1 exhibits an output power Pout of
about 1.5 dB and a power-added efficiency PAE of about 10%. This
means that the characteristics can be significantly improved with
the radio frequency power amplifier 1.
The reason why the characteristics are significantly improved is
that a potential increase at the connection point P between the
bridge resistor R and the resistors Ra1 through Ran compensates for
the voltage drop at the resistors Ra1 through Ran. In addition, it
is notable that the potential increase at the connection point P
can be used to increase the resistance values of the resistors Ra1
through Ran and thus to improve the operation uniformity among the
transistors TR1 through TRn.
As described above, the radio frequency power amplifier 1 according
to the first embodiment of the present invention can provide both
of a sufficient destruction resistance and superb radio frequency
characteristics by inserting the bridge resistor R.
In the first embodiment, one bridge resistor R is inserted.
Alternatively, a radio frequency power amplifier 1' shown in FIG. 4
includes bridge resistors R1 through Rn respectively provided in
correspondence with the transistors TR1 through TRn. With such a
structure also, substantially the same effect is provided.
Referring to FIG. 5, a radio frequency power amplifier 1'' includes
one capacitor C acting as an assembly of the plurality of
capacitors C1 through Cn. With such a structure, substantially the
same effect is provided.
Second Embodiment
FIG. 6 shows a circuit configuration of a radio frequency power
amplifier 2 according to a second embodiment of the present
invention. As shown in FIG. 6, the radio frequency power amplifier
2 according to the second embodiment includes transistors TR1
through TRn, capacitors C1 through Cn, resistors Ra1 through Ran,
resistors Rb1 through Rbn, and a bridge resistor R. As can be
appreciated from FIG. 6, the radio frequency power amplifier 2
according to the second embodiment includes the resistors Rb1
through Rbn in addition to the structure of the radio frequency
power amplifier 1 according to the first embodiment.
The resistors Rb1 through Rbn each have a very small resistance
value, and respectively inserted between a connection point of the
corresponding capacitor among the capacitors C1 through Cn and the
corresponding resistor among the resistances Ra1 through Ran, and
the base of the corresponding transistor among the transistors TR1
through TRn. Thus, the resistors Rb1 through Rbn act as base
ballast resistances respectively for the transistors TR1 through
TRn.
As described above, the radio frequency power amplifier 2 according
to the second embodiment of the present invention includes the
resistors Rb1 through Rbn each having a very small resistance value
at the bases of the transistors TR1 through TRn. Owing to such a
structure, the radio frequency power amplifier 2 stabilizes the
transistors TR1 through TRn and suppresses an unnecessary
oscillation thereof in addition to providing the effect described
above in the first embodiment. Needless to say, the structure of
the second embodiment is applicable to the structure including a
plurality of bridge resistors R1 through Rn shown in FIG. 4 or the
structure including a single capacitor C shown in FIG. 5.
Third Embodiment
FIG. 7 shows a circuit configuration of a radio frequency power
amplifier 3 according to a third embodiment of the present
invention. As shown in FIG. 7, the radio frequency power amplifier
3 according to the third embodiment includes transistors TR1
through TRn, capacitors C1 through Cn, resistors Ra1 through Ran,
resistors Rc1 through Rcn, and a bridge resistor R. As can be
appreciated from FIG. 7, the radio frequency power amplifier 3
according to the third embodiment includes the resistors Rc1
through Rcn in addition to the structure of the radio frequency
power amplifier 1 according to the first embodiment.
The resistors Rc1 through Rcn each have a very small resistance
value, and inserted between the corresponding capacitor among the
capacitors C1 through Cn, and a connection point of the
corresponding resistor among the resistors Ra1 through Ran and the
base of the corresponding transistor among the transistors TR1
through TRn. Thus, the resistors Rc1 through Rcn act as base
ballast resistors respectively for the transistors TR1 through
TRn.
As described above, the radio frequency power amplifier 3 according
to the third embodiment of the present invention includes the
resistors Rc1 through Rcn each having a very small resistance value
at the bases of the transistors TR1 through TRn. Owing to such a
structure, the radio frequency power amplifier 3 stabilizes the
transistors TR1 through TRn and suppresses an unnecessary
oscillation thereof in addition to providing the effect described
above in the first embodiment. Needless to say, the structure of
the third embodiment is applicable to the structure including a
plurality of bridge resistors R1 through Rn shown in FIG. 4 or the
structure including a single capacitor C shown in FIG. 5.
Fourth Embodiment
FIG. 8 shows a circuit configuration of a radio frequency power
amplifier 4 according to a fourth embodiment of the present
invention. As shown in FIG. 8, the radio frequency power amplifier
4 according to the fourth embodiment includes transistors TR1
through TRn, capacitors C1 through Cn, resistors Ra1 through Ran,
transmission lines TL1 through TLn, and a bridge resistor R. As can
be appreciated from FIG. 8, the radio frequency power amplifier 4
according to the fourth embodiment includes the transmission lines
TL1 through TLn in addition to the structure of the radio frequency
power amplifier 1 according to the first embodiment.
The transmission lines TL1 through TLn are each inserted between an
input terminal for a radio frequency signal (RF) and the
corresponding capacitor among the capacitors C1 through Cn. The
transmission lines TL1 through TLn are resistance components
generated by an inter-device line when the circuits of the radio
frequency power amplifiers are actually laid-out on a semiconductor
chip. The transmission lines TL1 through TLn generate
self-resonance with the capacitors C1 through Cn and reduce the
impedances between the input terminal for the radio frequency
signal (RF) and the bases of the transistors TR1 through TRn. Since
the radio frequency signal (RF) passes through the radio frequency
amplifier 4 more easily, the radio frequency characteristics
including the power gain are improved. Instead of the transmission
lines TL1 through TLn, general resistors may be used.
As described above, the radio frequency power amplifier 4 according
to the fourth embodiment of the present invention further improves
the radio frequency characteristics by effectively using the
transmission lines TL1 through TLn. The area size of the capacitors
C1 through Cn can be reduced while providing the same level of
radio frequency characteristics, which contributes to the reduction
of the chip size. Needless to say, the structure of the fourth
embodiment is applicable to the structure including a plurality of
bridge resistors R1 through Rn shown in FIG. 4 or the structure
including a single capacitor C shown in FIG. 5.
Fifth Embodiment
FIG. 9 shows a circuit configuration of a radio frequency power
amplifier 5 according to a fifth embodiment of the present
invention. As shown in FIG. 9, the radio frequency power amplifier
5 according to the fifth embodiment includes amplifiers 50 through
52, a plurality of collector bias circuits 53, a plurality of bias
circuits 55, an input matching circuit 56, a first inter-stage
matching circuit 57, a second inter-stage matching circuit 58, and
an output matching circuit 59.
The amplifiers 50 through 52 each have a structure of any of the
radio frequency power amplifiers 1 through 3 according to the first
through third embodiments. Each of the plurality of bias circuits
55 connected to the amplifiers 50 through 52 is, for example, the
bias circuit (Bias) described in the first embodiment. Each of the
plurality of collector bias circuits 53 includes a transmission
line (e.g., .lamda./4 line), an inductor or a capacitor, and
supplies a bias voltage to the collectors of the transistors TR1
through TRn. The input matching circuit 56, the first inter-stage
matching circuit 57, the second inter-stage matching circuit 58,
and the output matching circuit 59 are for matching the different
impedances of the transistors and providing radio frequency
characteristics. The input matching circuit 56, the first
inter-stage matching circuit 57, the second inter-stage matching
circuit 58, and the output matching circuit 59 each include a
transmission line, an inductor or a capacitor.
The radio frequency power amplifier 5 including a plurality of
stages as described above can also provide both of a sufficient
destruction resistance and superb radio frequency characteristics
by using the radio frequency power amplifiers 1 through 3 according
to the present invention. Especially, the radio frequency power
amplifier 5 can minimize the characteristic differences among the
different stages of amplifiers. Therefore, the radio frequency
power amplifier 5 can be applied to a low distortion amplifier
having improved linearity by appropriately adjusting the
relationship between the input voltage and the bias voltage.
While the invention has been described in detail, the foregoing
description is in all aspects illustrative and not restrictive. It
is understood that numerous other modifications and variations can
be devised without departing from the scope of the invention.
* * * * *